The present invention is generally directed to a system and method for varying characteristics of electrical signals for nerve stimulation therapy.
Electrical therapy has long been used in medicine to treat pain and other conditions. One such therapy is transcutaneous electrical nerve stimulation (TENS). This therapy involves the delivery of electrical energy through patch electrodes placed on the surface of a patient""s skin to treat pain in tissue beneath and around the location of the patch electrodes. The electrical energy is typically delivered to the patient in a waveform that varies according to a single preset frequency or a limited frequency combination. For example, some conventional TENS devices can provide a signal that oscillates in a single step between a high frequency and a low frequency.
The relationship between waveform frequency and efficacy varies from patient to patient and from condition to condition. Previous art TENS studies therefore vary greatly in their conclusions regarding the efficacy of different TENS waveforms. For example, a review of 46 published TENS studies showed a wide variation in pain relief effect. It is difficult (if not impossible) to determine from these studies which waveform frequency should be used to treat a new patient or a prior patient with a new condition.
Some studies have attempted to determine the relationship between waveform frequency and the mechanism underlying the therapeutic effect, such as pain relief. For example, one study of 37 patients determined that TENS applied at a relatively low frequency (2 Hz) increased the concentration of an enkaphalin pain reliever in patients"" cerebral spinal fluid (CSF), while TENS applied at a relatively high frequency (100 Hz) increased the concentration of a dynorphin pain reliever in the CSF. These studies did not attempt to correlate the increased concentrations of these substances in the CSF with pain relief effect, nor did they suggest which patients would benefit more from one frequency or the other or which conditions were best treated at one frequency or the other.
Electrical therapy to treat pain and other conditions may also be delivered percutaneously. This percutaneous approach is commonly referred to as Percutaneous Neuromodulation Therapy (PNT) or Percutaneous Electrical Nerve Stimulation (PENS). Like the TENS studies, however, published studies describing percutaneous electrical therapy have focused on limited patient populations and on limited frequencies and frequency combinations. These studies do not guide clinicians in the treatment of any particular patient with unknown electrical therapy response characteristics and an unknown condition underlying the apparent symptoms.
Thus, a significant drawback of conventional electrical therapy approaches is that they fail to provide a therapeutic regime that will be efficacious across entire populations of patients and across a variety of patient conditions. For example, some conventional approaches require trial and error testing of the patient to determine which waveform frequency would be best to treat that patient""s condition, thereby consuming scarce medical personnel time and delaying the possible therapeutic effect for the patient. Furthermore, conventional electrical therapy systems take a xe2x80x9cone size fits allxe2x80x9d treatment approach with widely varying results.
The present invention is directed toward methods and systems for delivering electrical therapy to a recipient. In one aspect of the invention, the method can include coupling an electrode (such as a percutaneous probe) to the recipient and applying electrical pulses to the electrode. The method can further include varying a frequency of the electrical pulses from a first value of no more than about 4 Hz to a second value of no less than about 10 Hz and back to the first value over a period of time greater than 6 seconds. The frequency of the electrical pulses can be automatically varied and, in a further aspect of the invention, can be automatically varied in response to a signal received from the recipient. The method can further include varying a frequency of the electrical pulses over a first range of frequencies for a first period of time greater than 6 seconds, and varying the frequency over a second period of a time approximately the same as the first period of time. The frequency of the electrical signal pulses can be varied over the course of a session having a duration of from about 20 minutes to about 45 minutes.
In another aspect of the invention, the method can include selecting a first session time for applying a first electrical signal to an electrode coupled to a recipient. The method can further include applying pulses of the first electrical signal according to a first schedule for pulse frequency, duration and period. The method can further include selecting a second session time different than the first session time and applying pulses of a second electrical signal according to a second schedule. The manner in which at least one of the frequency, duration and period varies during the second schedule is based on the second session time and is different for the second schedule than for the first schedule.
Another aspect of the invention is directed toward a computer-implemented method for controlling administration of electrical therapy to a recipient. The method can include receiving an indication of an initiation of a therapy session and receiving a schedule for varying a frequency of electrical pulses as a function of time. The method can further include directing a variation of a frequency with which electrical pulses are applied to an electrode according to the schedule while the electrode is coupled to the recipient. The method can further include receiving an indication of an end of the therapy session, and directing the electrical pulses to cease. The schedule can be retrieved from a computer-readable medium and can include a first frequency value of no more than about 4 Hz, a second frequency value of no less than about 10 Hz, and a time period value. Directing a variation of the frequency can include directing a frequency of the electrical pulses to vary from the first frequency value to the second frequency value during the time period.